Case of the Month ...

Case History

The patient is an 18 year-old white male who presented with a 4.5 cm right anterior cervical mass, which he first discovered 2 months ago. The mass was firm, mobile and non-tender. He complained of a sore throat and right ear pain, but denied having night sweats, fever or weight loss. The mass did not resolve with antibiotics. Fine needle aspiration of the mass was performed.

Which of the following is NOT a characteristic cytomorphologic feature of this tumor?

Basaloid cells

Squamous differentiation

Calcifications

Sharply demarcated cell clusters with peripheral palisading

The two key cytomorphologic features of this tumor are:

Atypical squamous cells and basaloid cells

Anucleated squamous cells and calcium deposits

Basaloid cells and ghost cells

Anucleated cells and foreign body giant cells

Which of the following is true regarding this lesion?

It is not associated with overlying skin discoloration

Usually presents in head, neck, face, and upper extremities of young patients

Affects males more than females

Preoperative clinical diagnosis is often accurate

Discussion:

Pilomatrixoma (pilomatricoma, calcifying epithelioma of Malherbe) is a tumor of hair follicle origin matrix that is almost always benign. It usually occurs in the first two decades of life and shows a female predominance. A second peak occurs in adults between 50 and 65 years of age. The most common sites for pilomatrixoma are the head, neck, face, and upper extremities. It usually presents as a painless lump and is often misdiagnosed preoperatively as an epidermoid cyst. Other preoperative clinical diagnoses include adnexal tumors, granulomatous inflammation, and malignant neoplasms including squamous cell carcinoma, small round blue cell tumors, and malignant skin appendage tumors. It may also be mistaken for a salivary gland tumor. Clinically, pilomatrixoma presents as a firm/hard nodule that may have bluish-red discoloration of the overlying skin.

Cytomorphologic findings of pilomatrixoma on fine-needle aspiration (FNA) include small to intermediate-size basaloid cells, often in dense clusters with overlapping nuclei, with high nuclear to cytoplasmic ratio and scant cytoplasm. The basaloid cells may also be arranged singly or in loosely cohesive monolayer sheets with irregular edges. Basaloid cells demonstrate fine, granular chromatin and in some cases, hyperchromatic, coarsely granular chromatin that is even in distribution. Nuclear molding has also been described in some cases. Conspicuous nucleoli may be observed. Squamous differentiation identified by the presence of cell junctions and intercellular bridging may also be seen. Squamous cells with small, dark nuclei and sparse, dense cytoplasm may be present in the center of basaloid cell clusters. Ghost or shadow cells are another important feature and are present both in clumps or as single anucleated squamous cells that often have a refractile quality. Other components observed in FNA include multinucleated giant cells, nucleated squamous cells, keratin clumps, and calcium deposition. The background is frequently hemorrhagic with amorphous debris and chronic inflammation. The two key elements in the cytologic diagnosis of pilomatrixoma are basaloid cells and ghost cells.

Histologic features of pilomatrixoma include a well-demarcated lesion comprised of basaloid cells showing squamous differentiation located at the periphery of the lesion with gradual transition to the more centrally located ghost cells. Calcium deposits, ossification, and foreign body giant cells may be present. High mitotic activity is a feature of the basaloid cells, but does not indicate malignancy. Rather, cytologic atypia, local aggressive behavior, vascular invasion, and infiltrative basaloid nodules are indicative of a malignant pilomatrixoma (pilomatrix carcinoma).

The differential diagnosis of pilomatrixoma includes adnexal cysts, parotid tumors, calcified lymph nodes, hemangioma, and malignant tumors including squamous cell carcinoma, basal cell carcinoma, Merkel cell carcinoma, and other small round blue cell tumors such as lymphoma/leukemia, Ewing’s/peripheral neuroectodermal tumor, neuroblastoma/retinoblastoma, and rhabdomyosarcoma. Mitotic figures and a background containing amorphous debris and inflammatory cells that resembles tumor necrosis are features that may be mistaken for malignancy. In contrast to squamous cell carcinoma, pilomatrixoma shows cells lacking definite malignant features and contain ghost cells. In basal cell carcinoma, the basaloid cells are arranged in tight clusters with palisading of the peripheral cells. Nucleoli are small to absent and ghost cells and multinucleated giant cells are not present. Also, mature nucleated squames are rarely seen in basal cell carcinoma.

FNA of Merkel cell tumor demonstrates a dispersed monomorphic population of atypical small cells with coarsely granular, irregular chromatin and inconspicuous nucleoli. In addition, ghost cells, nucleated squames, and multinucleated giant cells are not features of Merkel cell tumor.

Baslaoid cells may be a prominent component of some benign and malignant salivary gland tumors; however, many of these tumors (e.g., pleomorphic adenoma and adenoid cystic carcinoma) also show a characteristic stroma that is helpful to arrive at a correct diagnosis.